1. Field of the Invention
The present invention relates to electromagnetically actuable proportional hydraulic valves and, more particularly, to electromagnetically actuable proportional hydraulic valves having a magnetic part comprising an electrically triggerable coil, a stationary core protruding into the interior of the coil, an armature guided displaceably and acted upon by the coil, which armature is coupled with a closing member, and a valve part provided with at least one inflow conduit, at least one return conduit, at least one work conduit and at least one valve seat, the valve seat being in operative communication with the closing member so as to control a pressure-fluid communication between the work conduit and the return conduit.
2. Description of the Related Art
Among other purposes, electromagnetically actuatable proportional hydraulic valves are used to regulate the pressure in hydraulic circuits, for instance in automatic transmissions of motor vehicles. One such proportional valve is already known as an example from German Utility Model DE-GM 94 10 219. This proportional valve has a magnetic part whose armature acts on a closing member of a valve part and with it forms a flat seat valve. Flat seat valves are distinguished in particular by their insensitivity to errors of alignment between the armature and the closing member; however, because of flow conditions of the closing member, they do tend to vibrate, which over the course of operation can cause leaks and wear. If no counteracting provisions are taken at the closing member, its function is furthermore sharply dependent on the temperature, that is, on the viscosity and hence the viscous friction, of the pressure fluid. This can lead to irregular pressure/current characteristic curves of the proportional valve. Both effects are undesirable, since they impair the functional properties of a hydraulic circuit connected to these valves.
It is an object of the present invention to provide an electromagnetically actuable proportion hydraulic valve of the above-described kind, which has improved stability when subjected to temperature variations and under flow conditions that tend to produce vibrations.
This object and others, which will be made more apparent hereinafter, are attained in an electromagnetically actuatable proportional hydraulic valve, having a magnetic part comprising an electrically triggerable coil, a stationary core protruding into the interior of the coil, an armature guided displaceably and acted upon by the coil, which is coupled with a closing member and a valve part provided with at least one inflow conduit, at least one return conduit, at least one work conduit and at least one valve seat, the valve seat being in operative communication with the closing member in order to control a pressure-fluid communication between the work conduit and the return conduit.
According to the invention the closing member, at least in the region of its end toward the valve seat, has a substantially conical sealing body, whose smaller end face is facing toward the valve seat, and the sealing body has at least one flow separation edge on its end remote from the valve seat.
By comparison, the electromagnetically actuable proportional hydraulic valve according to the invention has the advantage that it behaves substantially in a more stable manner in the face of temperature factors and flow-dictated inducements to vibrations. The pressure/current characteristic curves of the proportional valve have a more constant and steadier course as a result, thus minimizing the expense for programming triggering for the proportional valve. The sealing properties and wear behavior of the proportional valve of the invention are improved. Sensors to detect and compensate for temperature factors and hydraulic circuits can be dispensed with. Further advantages or advantageous refinements of the invention will become apparent from the dependent claims and the following description.
Two exemplary embodiments with particularly advantageous closing members are defined by the dependent claims. In one embodiment the sealing body has a cup-shaped cross section, with a curved face end oriented toward the valve seat. In this embodiment the closing member is distinguished by its simple form and economical manufacture. In other embodiments the armature acts on the closing member by means of a tappet and the sealing body is connected to a guide region that cooperates with a guide member of the housing by means of a connecting portion. In these other embodiments the closing member is especially insensitive to errors of alignment, because its guidance is uncoupled from the armature. In the other dependent claims, features that are advantageous from a production standpoint are disclosed, along with especially suitable usage areas for the proportional valves of the invention.